fix(scripts): Log big fat deprecation warnings for addon_* scripts

These have been replaced by cloud config.
fix(virtfs): Only handle 'metadata' virtfs volume.

This has been replaced by config drive in coreos-cloudinit, those
volumes are named 'config-2'. The name 'metadata' was used by both our
QEMU wrapper script and libvirt documentation.
Merge pull request #74 from marineam/units

Deprecating the deprecated